A method to reduce NO x Reburning ultrafine pulverized coal unit

Abstract

This invention relates to a method for reducing NO x This re-combustion ultrafine pulverized coal device belongs to the field of pulverized coal combustion technology. It includes an air-coal mixing distributor, a re-combustion fan, a pulverizer, and a re-combustion burner. The outlets of the re-combustion fan and the pulverizer are connected to the gas inlet and pulverized coal inlet of the air-coal mixing distributor, respectively. The re-combustion fuel transport medium is recirculated flue gas. The re-combustion burner is located in the re-combustion zone inside the furnace and includes four sets of direct-flow burner nozzles. The mixture outlet of the air-coal mixing distributor is connected to each of the four sets of direct-flow burner nozzles. The four sets of direct-flow burner nozzles are located at the four corners of the furnace, and their ejection directions are tangential, resulting in a tangential flow field distribution of the mixture gas flow inside the furnace. This device solves the problem of current pulverized coal boilers using a swirl-type main burner paired with a swirl-type re-combustion burner, which leads to reduced NO₂ levels. x The problem of poor emission performance.

Description

Technical Field

[0001] This invention belongs to the field of pulverized coal combustion technology, specifically relating to a method for reducing NO. x Reburning ultrafine pulverized coal device. Background Technology

[0002] To control NOx emissions from coal-fired boilers x Currently, emissions are primarily reduced using low-NOx combustion technology, a staged air combustion method. This aims to further reduce NOx emissions. x The formation of NO can be achieved using staged reburning technology. This technology works by injecting reburning fuel to produce intermediate products such as CH₄·, which then dissipate the NO generated in the main combustion zone. x Restored to N2.

[0003] In existing technologies, natural gas or pulverized coal are commonly used as reburning fuels. Natural gas is more expensive and less economical, so pulverized coal is often used as the reburning fuel. When pulverized coal is used as the reburning fuel, in order to ensure the adoption of staged reburning technology to reduce NO... x To achieve optimal results, ultrafine bituminous coal with high volatile matter should be used. For furnaces with swirl burners as the main burner, swirl burners are often used for reburning ultrafine pulverized coal. However, while swirl burners result in strong initial mixing, rapid gas flow decay, insufficient penetration depth in the later stages, and poor filling of the entire furnace cross-section. This leads to uneven mixing of the reburned fuel and the rising flue gas from the main combustion zone, limiting the reduction of NOx. x The reduction efficiency and effect of NO reduction are important; therefore, selecting a suitable reburner type and structure is crucial for reducing NO through reburning. x The effect is very important. Summary of the Invention

[0004] This invention overcomes the shortcomings of existing technologies and proposes a method for reducing NO. x Re-burning ultrafine pulverized coal device; solves the problem of current pulverized coal boilers using a swirl-type main burner paired with a swirl-type re-burning burner, which leads to reduced NO₂ levels. x The problem of poor emission performance.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution.

[0006] A method to reduce NO xThe reburning ultrafine pulverized coal device includes an air-coal mixing distributor, a reburning blower, a pulverizer, and a reburning burner. The inlet of the pulverizer is connected to the reburning pulverized coal silo via a pipeline. The reburning pulverized coal silo stores ultrafine pulverized coal. The outlet of the reburning blower and the outlet of the pulverizer are respectively connected to the gas inlet and the powder inlet of the air-coal mixing distributor. The reburning burner is arranged in the reburning zone inside the furnace. The reburning burner includes four sets of DC burner nozzles. The mixed material outlet of the air-coal mixing distributor is connected to the four sets of DC burner nozzles via four conveying pipelines. The four sets of DC burner nozzles are respectively located at the four corners of the furnace. The ejection direction of the four sets of DC burner nozzles is tangential, so that the mixed material airflow ejected from the four sets of DC burner nozzles is organized into a tangential flow field distribution inside the furnace.

[0007] Furthermore, inside the furnace, along the direction of flue gas flow, there are a main combustion zone, a re-combustion zone, and a burnout zone, with the main combustion zone located upstream of the re-combustion zone and the re-combustion zone located upstream of the burnout zone.

[0008] Furthermore, a main burner, which is a swirl burner, is arranged in the main combustion zone of the furnace.

[0009] Furthermore, the air inlet of the reburning blower is connected to the flue gas source via a pipeline.

[0010] Furthermore, the DC burner nozzle has a rectangular structure with a height-to-width ratio of 1 to 1.5.

[0011] Furthermore, both the reburning blower and the pulverizer are controlled by frequency converters.

[0012] The beneficial effects of this invention compared to the prior art are as follows: (1) This invention targets furnaces with swirl burners as the main burner, breaking away from the traditional technology that "reburning must be paired with swirl burners." It creatively employs four-corner arranged DC burner nozzles as the reburning injection device. Utilizing the advantages of strong mixing and turbulence from tangential combustion at the four corners, it solves the problems of poor mixing and uneven coverage in the later stages of swirl reburning burners, achieving uniform distribution of reburning fuel across the entire furnace cross-section and significantly improving NO₂ levels. x The mixing strength and reaction effect with the reducing agent.

[0013] (2) This invention uses ultrafine pulverized coal as the reburning fuel. Ultrafine pulverized coal has a high volatile content and a fast release rate, which significantly shortens the start-up time of the reduction reaction and enhances the reaction effect. It is perfectly matched with the high temperature and high turbulence field formed by the four corner-arranged DC burner nozzles. Flue gas is used as the transport medium to replace the traditional air, which fundamentally isolates the introduction of oxygen into the reburning zone and maintains the optimal reducing atmosphere, thereby maximizing the reduction of NO. x reduction.

[0014] (3) This invention is equipped with a reburning fan and a pulverizer with variable frequency control. By adjusting the frequency of the reburning fan, the amount of flue gas delivered can be independently controlled, thereby adjusting the flow field distribution of the reburning air; by adjusting the frequency of the pulverizer, the amount of reburning fuel can be independently controlled. This dual-frequency independent control allows the reburning system to adjust according to the boiler load and initial NO. x Concentration, online optimization of injection momentum and fuel quantity to ensure optimal NO concentration under different operating conditions. x Reduction efficiency. Attached Figure Description

[0015] The present invention will now be described in further detail with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram showing the arrangement of the furnace and the nozzles of the four sets of DC burners; Figure 3 This is a schematic diagram showing the relative positions of the main combustion zone, recombustion zone, and burnout zone inside the furnace. Among them, 1 is the reburning powder bin, 2 is the powder feeder, 3 is the reburning blower, 4 is the air-powder mixing distributor, 5 is the material conveying pipeline, 6 is the DC burner nozzle, 7 is the main combustion zone, 8 is the reburning zone, 9 is the burnout zone, and 10 is the furnace. Detailed Implementation

[0016] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0017] like Figure 1 As shown in Figure 3, this invention provides a method for reducing NO x The reburning ultrafine pulverized coal device includes an air-coal mixing distributor 4, a reburning blower 3, a pulverizer 2, and a reburning burner. The outlet of the reburning blower 3 and the outlet of the pulverizer 2 are respectively connected to the gas inlet and the powder inlet of the air-coal mixing distributor 4. The reburning burner is arranged in the reburning zone 8 inside the furnace 10. The reburning burner includes four sets of DC burner nozzles 6. The mixed material outlet of the air-coal mixing distributor 4 is connected to the four sets of DC burner nozzles 6 through four conveying pipelines 5. The four sets of DC burner nozzles 6 are respectively set at the four corners of the furnace 10. The ejection direction of the four sets of DC burner nozzles 6 is tangentially arranged, so that the mixed material airflow ejected from the four sets of DC burner nozzles 6 is organized into a tangential flow field distribution inside the furnace 10.

[0018] Inside the furnace 10, along the flue gas flow direction, there are sequentially arranged a main combustion zone 7, a re-combustion zone 8, and a burnout zone 9, wherein the main combustion zone 7 is located upstream of the re-combustion zone 8, and the re-combustion zone 8 is located upstream of the burnout zone 9. A main burner, which is a swirl burner, is arranged in the main combustion zone 7 of the furnace 10. The burnout zone 9 is used to supplement the burnout air.

[0019] The air inlet of the reburning blower 3 is connected to the flue gas source through a pipeline, and the reburning blower 3 draws the hot flue gas from the flue gas source into the air-coal mixing distributor 4 as a conveying medium.

[0020] The inlet of the pulverizer 2 is connected to the reburning pulverizer 1 via a pipeline, and the reburning pulverizer 1 stores ultrafine pulverized coal (V). daf The ultrafine pulverized coal (≥35%, fineness R90≤5%) is ground by a reburning fuel preparation system. The ultrafine pulverized coal inside the reburning pulverized coal bin 1 is transported to the air-coal mixing distributor 4 by the pulverizer 2.

[0021] By arranging four sets of DC burner nozzles 6 at the four corners of the furnace 10, the jets ejected from the DC burner nozzles 6 are ensured to have sufficient rigidity to resist the disturbance of rising flue gas. The DC burner nozzles 6 have a rectangular structure with a height-to-width ratio of 1 to 1.5. The horizontal axis of the DC burner nozzles 6 forms a specific angle with the normal direction of the two adjacent walls of the furnace 10, so that the four jets ejected from the four sets of DC burner nozzles 6 form an imaginary tangent circle of a specific diameter at the center of the reburning zone 8 of the furnace 10.

[0022] The working principle of this invention is as follows: Ultrafine pulverized coal is stored inside the reburning pulverized coal bin 1 and meteredly discharged into the air-pulverized coal mixing distributor 4 via the pulverizer 2. The reburning blower 3 draws flue gas from the flue gas source, which is then used as the conveying medium into the air-pulverized coal mixing distributor 4. After the ultrafine pulverized coal and flue gas are fully mixed inside the air-pulverized coal mixing distributor 4, a gas-solid two-phase flow is formed. Both the reburning blower 3 and the pulverizer 2 are controlled by frequency converters to precisely adjust the feed rate of the ultrafine pulverized coal and the flow velocity of the flue gas.

[0023] The gas-solid two-phase flow output from the air-coal mixing distributor 4 is divided into four equal parts through the conveying pipeline 5, and respectively delivered to the four sets of DC burner nozzles 6 at the four corners of the furnace 10. The coal powder concentration delivered to the DC burner nozzles 6 is controlled at 0.3~0.5 kg / kg. The four sets of DC burner nozzles 6 are arranged tangentially, so that the gas-solid two-phase flow injected into the furnace forms a tangential flow field distribution at the four corners in the reburning zone 8 of the furnace 10. By adjusting the frequency of the reburning fan 3, the ejection velocity of the DC burner nozzles 6 is controlled at 30m / s~40m / s to ensure a suitable tangential flow field distribution at the four corners. The ultrafine coal powder ejected from the DC burner nozzles 6 is used as reburning fuel, and the amount of reburning fuel is generally 5%-15% of the total fuel. The amount of reburning fuel is controlled by adjusting the frequency of the pulverizer 2.

[0024] High-speed flue gas-pulverized coal jets ejected from the four sets of DC burner nozzles 6 enter the recombustion zone 8 of the furnace 10 from the four corners of the furnace 10, forming a strong swirling field in the furnace 10. Under the action of high temperature and strong turbulence, the ultrafine pulverized coal instantly undergoes thermal decomposition, releasing a large amount of CH·, which reacts with NO-containing gases generated in the main combustion zone 7 and rises there. x The flue gas is fully mixed and reduced. After passing through the re-combustion zone 8, the flue gas enters the burnout zone 9, where the burnout air injected by the burnout air system replenishes the remaining air required for combustion, ensuring complete combustion of pulverized coal and ultimately achieving the dual goals of efficient denitrification and low fly ash carbon content.

[0025] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method to reduce NO x The device for re-combustion of ultrafine pulverized coal is characterized by: The furnace includes a coal-air mixing distributor (4), a reburning blower (3), a coal feeder (2), and a reburning burner. The inlet of the coal feeder (2) is connected to the reburning coal silo (1) via a pipeline, and ultrafine coal powder is stored inside the reburning coal silo (1). The outlet of the reburning blower (3) and the outlet of the coal feeder (2) are respectively connected to the gas inlet and the powder inlet of the coal-air mixing distributor (4). The reburning burner is located in the reburning zone (8) inside the furnace (10). The burner includes four sets of DC burner nozzles (6). The mixed material outlet of the air-coal mixing distributor (4) is connected to the four sets of DC burner nozzles (6) through four conveying pipes (5). The four sets of DC burner nozzles (6) are respectively located at the four corners of the furnace (10). The ejection direction of the four sets of DC burner nozzles (6) is arranged tangentially, so that the mixed material airflow ejected by the four sets of DC burner nozzles (6) is organized into a flow field distribution of tangential circles at the four corners inside the furnace (10).

2. A method for reducing NO according to claim 1 x The device for re-combustion of ultrafine pulverized coal is characterized by: Inside the furnace (10), along the direction of flue gas flow, there are a main combustion zone (7), a re-combustion zone (8), and a burnout zone (9), in sequence. The main combustion zone (7) is located upstream of the re-combustion zone (8), and the re-combustion zone (8) is located upstream of the burnout zone (9).

3. A method for reducing NO according to claim 2 x The device for re-combustion of ultrafine pulverized coal is characterized by: A main burner is arranged in the main combustion zone (7) of the furnace (10), and the main burner is a swirl burner.

4. A method for reducing NO according to claim 1 x The device for re-combustion of ultrafine pulverized coal is characterized by: The air inlet of the reburning blower (3) is connected to the flue gas source through a pipeline.

5. A method for reducing NO according to claim 1 x The device for re-combustion of ultrafine pulverized coal is characterized by: The nozzle (6) of the DC burner has a rectangular structure with a height-to-width ratio of 1 to 1.

5.

6. A method for reducing NO according to claim 1 x The device for re-combustion of ultrafine pulverized coal is characterized by: Both the reburning blower (3) and the powder feeder (2) are controlled by frequency conversion.

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